The present invention relates to simultaneous two-way data transmission on transmission channels, and more particularly to the echo cancellation technique.
Echo cancelling devices provide an estimate of the echo and subtract it from the perturbated signal.
This estimate of the echo signal is usually made at the instants of sampling by adjusting the coefficients C.sub.k of the echo cancelling device. This adjustment is usually made by the gradient algorithm. Such a technique has been described for example in the article by Muller in IEEE Transactions on Communications, Vol. 24, No. 9, Sept. 76, pages 956-962.
Adjustments employing the gradient algorithm are simple to carry out but the convergence of the echo cancelling device using this process is not very rapid.
It is an object of the present invention to improve the rapidity of the convergence of the echo cancelling devices depending on the types of exploitation used, by employing an initialization device. Moreover, the initialization device according to the invention enables the remote echo to be located and is independent of the algorithm employed.
The initialization device according to the invention allows an initialization of any echo cancelling device according to a procedure such that each modem successively emits, and initializes its own echo cancelling device in the absence of a signal coming from the remote end. According to such a procedure, each modem emits an appropriate sequence enabling it to cancel its echo, the remote modem not emitting.